Focusing on the role of efficiency and novelty design themes, this paper examines how (a) the initial business model of a start-up, (b) the subsequent changes in the design themes and (c) the combinative effect of efficiency and novelty (contextual ambidexterity) impact a start-up's growth performance. The study is based on a survey involving 267 new ventures from high-tech industries. The results highlight the importance of pursuing higher efficiency over the life cycle of a start-up, although not at the moment of its establishment. In relation to business model ambidexterity, the findings highlight the different effect that contextual ambidexterity can have on the growth performance of a start-up firm in different stages of its life cycle. While initial ambidexterity is found to have a negative effect on growth performance, successive increases in the level of ambidexterity have a positive influence on growth.